| Criteria | Marks |
|---|
| Provides a comprehensive discussion of differences in the global distribution of malaria and its vector; refers to the stimulus to support arguments; provides reasons for presence of vector but no disease and absence of vector but disease located | 7 |
| Provides a thorough discussion of differences in the global distribution of malaria and its vector; refers to the stimulus to support arguments; provides reasons for presence of vector but no disease and/or absence of vector but disease located | 6 |
| Provides a discussion of differences in the global distribution of malaria and its vector; refers to the stimulus; provides reasons for presence of vector but no disease and/or absence of vector but disease located | 4–5 |
| Provides reason(s) for differences or correlation in global distribution of disease and vectors | 2–3 |
| Provides some relevant information | 1 |
Sample answer:
A pathogen that relies on transmission by a vector such as a mosquito, for example the malaria parasite, will occur mainly in areas where the vector occurs. However, there are areas identified in Map 2 where malaria occurs but the mosquito does not, for example northern Africa. It is possible that either there is insufficient data on the mosquito in those areas, or humans carrying the parasite have travelled into them on a regular basis, maintaining the disease in the population. Although international travel may bring malaria cases to other countries where the mosquito does not occur such as Australia, the numbers of cases remain small, are treated promptly and the disease ceases to circulate.
On the other hand, there are some countries in which the mosquito is found but no disease occurs, for example Europe. In these cases, public health measures could have been effective in reducing or eliminating malaria despite the presence of the mosquito vector. Strategies that prevent transmission by the vector would be effective in reducing the incidence of disease. For example, pesticides may be used to reduce mosquito populations and hence reduce spread of disease, or insect bites might be prevented by use of bed nets/ fly screens.
Other strategies that kill the parasite or prevent its survival in a new host would also be effective and may be responsible for large areas of the world not having malaria cases despite the presence of the vector, such as North America. For example widespread use of pharmaceuticals that target the malaria parasite could be used. This may only be available to wealthier populations such as USA.
Answers could include:
- Prophylactic drugs prior to travel to new areas
- Use of gene drives to reduce mosquito populations.
